Rare earth oxides and compound oxides comprising rare earth elements are widely used as functional inorganic materials such as phosphor, solid electrolyte, superconducting membrane, catalyst, ceramics and optical glass. For producing the rare earth oxides, rare earth alkoxides have been conventionally used as precursory material.
JP-A-7-285969 discloses a process for preparation of a rare earth alkoxyalkoxide. There are, however, some problems in this process. In the disclosed process, a rare earth carboxylate is caused to react with an alkali metal alkoxyalcoholate. As the alkali metal alkoxyalcoholate (namely, as a starting material of the process), an unstable alkali metal alkoxyalkoxide such as sodium alkoxyalkoxide is used. In addition, it is difficult to isolate and remove alkali metal carboxylate, that is a by-product of the reaction. Further, the rare earth carboxylate, that is another starting material of the process, must be beforehand made anhydrous. It is known that a pure anhydrous rare earth carboxylate can not be easily obtained by a simple procedure. If heated to dry by normal procedure, the hydrated rare earth carboxylate often decomposes.
Leblanc et al. [Tetrahedron Letters, vol. 32(1991), No. 21, pp. 2355-2358] disclose a process for preparation of a rare earth isopropoxide. In the process, a hydrated rare earth carboxylate is successively reacted with orthoformate, with 2-propanol and with n-butyl lithium. In this process lithium chloride is formed as a by-product. The lithium chloride precipitates in the form of very fine crystallite which is not easily separated from the product by filtration, and hence is liable to remain in the filtrate together with the product. Accordingly, in order to obtain a pure rare earth isopropoxide, it is necessary to repeat the purification procedures. As a result, troublesome procedures are indispensable, and the production yield is often low.
IEEE Transactions on Nuclear Science, vol. 47(2000), No. 6, pp. 1781-1786 discloses a process for preparation of lutetium isopropoxide. In the process, lutetium metal and isopropanol are reacted under nitrogen gas atmosphere in the presence of mercury chloride (catalyst). This process, however, has some problems. The mercury compound is harmful to the environment, and the rare earth metal is so expensive and so easily oxidized that it has to be treated very carefully.